Tear apart cannula

ABSTRACT

This invention relates to a flexible cannula comprising material which tears readily in a longitudinal direction and can thus be easily removed by pulling tabs on opposite sides of the cannula apart after the catheter or other device has been inserted into the body.

This is a continuation, of application Ser. No. 965,703 filed Dec. 1,1978, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a cannula used as an aid forinsertion of catheters and other instruments into the body and moreparticularly to a cannula that is easily removed after the insertion iscompleted.

2. Brief Description of the Prior Art

It is desirable that after a catheter or other body probe device hasbeen inserted into place within a blood vessel that the apparatus usedto aid the insertion is easily removable. When sharp devices such ashollow needles are left in place while the catheter or other device isbeing utilized, there is a danger that the needle may pierce through thevessel, causing tissue damage and rendering the catheter useless. Inassemblies where the needle is removable, this problem is alleviated;however, in these cases, the cannula which is used as a passageway intothe blood vessel, often cannot itself be easily removed when the probeor catheter that has been inserted has an enlarged proximal end. Theinability to easily remove the cannula is a disadvantage incircumstances when the inserted probe or catheter must remain in thebody for an extended period of time to be permanently implanted.

Various removable devices have been developed using frangible, hollowneedles (see Rubin, U.S. Pat. No. 3,382,872; MacGregor, U.S. Pat. No.3,550,591; Warren, U.S. Pat. No. 3,598,118 and Nerz, U.S. Pat. No.3,677,243). In these devices the hollow needle must have a largerdiameter to accommodate the catheter within the device. The larger sizeof the hollow needles can be a cause of additional tissue damage.Because of their rigidity and sharpness, these needles act as poorcannuli in situations where probes must be inserted and removedrepeatedly, and they cannot be used at all when the cannula must be usedas an aid in advancing the probe along the interior of the blood vessel.

Ansari, U.S. Pat. No. 3,545,443, utilizes dual hollow concentricneedles, each having a longitudinal slot. After insertion, the needleassembly is removed and twisted in such a manner that the slots arealigned. The catheter then can pass through the slots thus removing theneedle. This non-frangible assembly possesses many of the samedisadvantages that the other hollow needle devices have. In addition,because there are two hollow needles, an even larger needle diameter isnecessary to accomodate the same size catheter. The slots in the needlesmay also cause additional tissue damage and potentially may not be ableto effectively prevent blood loss and air emboli.

Gauthier, U.S. Pat. No. 3,094,122, uses a percutaneous needle that isinside the catheter. After insertion, the needle is removed lengthwisefrom the catheter. There are several restrictions upon this method. Theneedle must be longer than the catheter and the method is only adaptablefor insertion of hollow devices or catheters and cannot be used wherevarious probes and leads are to be inserted. Guttman, U.S. Pat. No.3,225,762, is similar to the Gauthier device except that the catheterhas a slot for removal of the needle after insertion. This eliminatesthe need to have a needle that is longer than the catheter, however,there may be undesirable leakage through the slit, particularly when thecatheter is bent at or near the slit. This invention also cannot be usedwhere the probe to be inserted within the vessel is not hollow.

Reilly, U.S. Pat. No. 3,570,485, provides a flexible cannula, placedover the percutaneous needle, that is slotted along its length. Afterinsertion, the needle is removed and the cannula can then act as asheath for insertion of the catheter or other device. After insertion ofthe probe, the cannula can be removed by sliding the catheter or otherdevice through the slit in the cannula. Although this invention isflexible and can be adopted for insertion of both catheters andnon-hollow probes, the longitudinal slot may not provide a blood orairtight seal. This problem may be reduced by increasing the thicknessof the cannula, however this would necessitate either the use of alarger puncture diameter or a smaller probe. Further, removal of thecannula requires gripping both the cannula and the inserted catheter andphysically pulling them apart. Applying such a force upon an object thatis partially inserted into the body may cause tissue damage. There isalso the potential of accidentally pulling the catheter out from itsinserted position.

The Reilly patent has a further limitation in its collapsibility. Whenthe Reilly cannula is empty prior to insertion of the catheter or probe,it collapses upon itself at the puncture site with the purpose ofpreventing blood loss. However, this attribute creates a disadvantage inthat a stiff catheter with a stiff tapered distal end is required inorder to reopen the cannula for reinsertion; therefore, flimsy andflexible leads, such as pacemaker leads and blunted tipped catheters,such as balloon tipped catheters, are unadoptable for use with thisdevice.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

The present invention is a flexible cannula that readily tears in alongitudinal direction along the length of the structure because itcomprises material that has a longitudinal orientation. Because it isflexible and hollow, it acts as a good cannula where devices must berepeatedly inserted, left within the body for a period of time, oradvanced along the interior of the vessel.

Because of its longitudinal orientation, the present invention canreadily be removed by tearing the structure along its length along twolongitudinal lines thereby splitting it into two halves. This is aparticular advantage where the lead or probe is to be permanentlyinserted and has large fittings or connectors on its proximal end suchthat the cannula cannot merely be slipped off the end of the probe.

Because no force needs to be applied to the partially inserted probewhen the cannula is split apart, the potential of accidentally pullingthe probe out from its desired position is diminished.

There are numerous specific applications in which the present inventioncan be utilized. One such application is for suprapubic insertion intothe bladder. Catheters used in this type of application normally haveenlarged proximal ends and remain in the body for prolonged periods oftime.

Another application is transvenous insertion of permanent pacemakerleads. Such leads separate into various electrodes at the proximal end,each electrode being significantly larger than the general diameter ofthe lead. After insertion of the distal end into the desired positionwithin the heart. These leads must themselves be implanted beneath theskin and connected to a power source. In the past, it has been thepractice to remove the sheath by slitting it with a scapel, in order toenable the implantation of the electrodes. Reference is made to"Percutaneous Insertion of a Permanent Transvenous Pacemaker Electrodethrough the Subclavion Vein" in the Canadian Journal of Surgery, vol.20, pg. 131 which is descriptive of this technique.

There are several existing techniques which can take advantage of thebenefits of the present invention. In one method the cannula is insertedinto a blood vessel about percutaneous needle. The needle is thenremoved, and a catheter or other probe device is inserted through thesheath and the combination is advanced into position. The cannula canthen be slipped out of the body and split by pulling a pair of tabs onthe end thereof thus being removed from the probe.

In another method, a hollow needle is inserted into a vessel. A wireguide is then passed through the needle into the interior portion of thevessel. The needle can then be withdrawn and the cannula with a dilatorinserted into the vessel over the wire guide. The assembly is advancedinto position and the dilator and wire guide are removed. A catheter orprobe can next be passed into the vessel through the cannula. Thecannula is withdrawn from the body and split apart thus being removedfrom about the probe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the splitable cannula in combination with adilator and wire guide.

FIG. 1A is an enlarged view similar to FIG. 1 of the structure of FIG. 1with portions broken away to show internal structure.

FIG. 1B is an enlarged fragmentary view of a portion of the structure ofFIG. 1.

FIG. 2 is a side view of a hollow percutaneous needle.

FIG. 3 through FIG. 11 are sections through a blood vessel showing aprocedure.

FIG. 3 illustrates the needle inserted within the blood vessel.

FIG. 4 shows a wire guide inserted into the vessel through the incisionneedle.

FIG. 5 shows the incision withdrawn from the puncture site.

FIG. 6 shows the wire guide percutaneously positioned within the bloodvessel.

FIG. 7 illustrates the splitable sheath and dilator combination insertedinto the vessel over the wire guide.

FIG. 8 illustrates the guide dilator and splitable cannula assemblyadvanced into the desired position within the vessel.

FIG. 9 shows the splitable cannula in position after the wire guide anddilator have been removed.

FIG. 10 illustrates a probe inserted within the splitable cannula.

FIG. 11 shows the cannula after being split into two parts.

FIG. 12 through FIG. 16 are sections through a blood vessel showing afurther procedure.

FIG. 12 illustrates a splitable cannula disposed about the incisionneedle and inserted in this manner into the blood vessel.

FIG. 13 shows the splitable cannula inserted within the vessel after theincision needle has been removed.

FIG. 14 illustrates the probe inserted within the cannula.

FIG. 15 shows the probe and splitable cannula combination advanced intothe desired position within the vessel.

FIG. 16 illustrates the cannula split into two parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention is shown in combinationwith a dilator and a wire guide in FIG. 1. The splitable cannula 10 isdisposed about the dilator 11 which, in turn, is disposed about the wireguide 12. The distal end 13 of the dilator is tapered for enlarging thepuncture site to accommodate the splittable cannula. Where the diameterof the splittable cannula is of a sufficiently large size, the dilatorthat is used has a second tapered portion 14. The tubular portion 15 ofthe splittable cannula has approximately uniform thickness and diameterexcept at its distal end 16 where there is a slight taper to create anappropriately snug fit with the dilator and also to facilitate theenlarging of the puncture site to accommodate the cannula. The proximalend 20 of the cannula is slit longitudinally producing two open endedslits at opposite sides of the tubular structure 21 and 22, thuscreating two tabs 23 and 24 which are attached to knobs 25 and 26 bybeing inserted between the screw 30 and 31 and socket 32 and 33 portionsof the knobs. At the proximal end of the dilator 11 is a knob-like clamp34 which maintains the two telescoping layers of the dilator 11 inposition.

FIG. 1B is a cross-sectional view showing a representative one of thetabs 23 attached to one of the knobs 25 which comprises a screw 30 andsocket 32 combination. The screw 30 is screwed into the socket 32 withthe end 23 in the socket. The force between the screw 30 and socket 32maintains the end of the tab in position. The knobs 25 and 26 are usedto aid in gripping the device when it is split apart.

FIGS. 3 through FIG. 11 shows a procedure whereby a probe havingrelatively large fittings on its proximal end is placed in position. Theprobe might be, for example, a catheter used to measure the flow ofsaline solution through the blood vessel. Such catheters have a balloonat the distal end which operates to close off the flow through the bloodvessel. This balloon is inflated by placing air into a fitting such asthe fitting 61. Another fitting such as fitting 62 might receive thesaline solution. Still another fitting such as the fitting 63 functionsto provide a coupling to a thermistor which measures the temperature ofthe saline solution blood mixture as it moves by the thermistor at stillanother point along the catheter.

FIG. 3 shows the percutaneous needle 40 inserted through the skin andbody tissue 50 and into a blood vessel 51. FIG. 4 shows the subsequentstep of inserting the wire guide 12 into the blood vessel 51 through theneedle 40. In FIG. 5 the needle 40 has been removed from the puncturesite leaving the wire guide as in FIG. 6. In FIG. 7 the splitablecannula 10 and dilator 11 combination is in the process of beinginserted into the blood vessel 51 about the wire guide 12. The cannula,dilator and wire guide combination have been advanced into the desiredposition in FIG. 8. In FIG. 9 the wire guide and dilator have beenremoved leaving the splittable cannula 10 in its desired position. FIG.10 shows a probe 60 being inserted into the blood vessel through thesplitable cannula 10. The probe elements 61, 62 and 63 are fittingswhich are permanently mounted on the proximal end of the probe 60. InFIG. 11 the splittable cannula has been removed from the puncture siteand split apart into two portions 70 and 71 and in this manner has beenseparated from the inserted probe.

In an alternative technique, the splittable cannula 10 may be insertedwithin the blood vessel 50 directly about the needle 40. FIG. 12 showsthis combination inserted within the blood vessel. FIG. 13 illustratesthe splitable cannula 10 inserted within the blood vessel after theincision needle 40 has been removed from the puncture site. FIG. 14illustrates the probe 60 introduced into the blood vessel 51 through thesplittable cannula 10. In FIG. 15 the probe 60 and cannula 10combination have been advanced into position. FIG. 16 shows the cannula10 withdrawn and split off leaving the probe in position.

Teflon (Teflon is the Dupont trademark for polytetrafluoroethylene) usedin the preferred embodiment is virgin material i.e., has not previouslybeen used, or reground. It is free of foreign matter and dye marks.These characteristics are required to ensure compatibility for insertioninto the body. Teflon is the preferred material because it can belongitudinally oriented through extrusion, although other plastics maybe useable. It is known, for example, that polyethylene obtains therequired longitudinal orientation characteristics if it is stretchedafter extrusion. However, polyethylene is not used in the preferredembodiment because it is understood that the orientation process forpolyethylene is more difficult to perform properly.

A standard extrusion process orientates the Teflon and forms it into thetubular shape of the cannula. The Teflon is blended with an extrusionaid or lubricant, preferably naphtha, and a thermally stable pigment.The pigment used may be any stable pigment that is acceptable forinsertion within the body. The naphtha normally comprises between 17 and20% by weight and the concentration of pigment should be less than 2%.Then, at temperatures above 75° F., the compound mixture is preformed.The object of preforming is to compact the powder into a cylinder whichis about one-third of the original volume. The preforming pressure isbetween 100 and 300 lbs/sq. in. The preform is then extruded through anextrusion die at pressures of approximately 20,000 psi. After extrusionthe Teflon tubing is passed through a drying oven at a graduatedtemperature increasing from 300° F. to 575° F. The heat from this ovenvaporizes the lubricant. The Teflon tubing is next led through asintering oven, at temperatures of at least 621° F., allowed to cool,and rolled onto spools.

In the manufacturing of the cannula, the Teflon tubing is cut offradially to define one end of the cannula and slit at that one end witha cutting instrument at opposite ends of the same end to form the twoopposed slits 20 and 21. This slitting operation creates the tabs 23 and24 which are used to pull apart the cannula and the slits define thelocation of the beginning of the tears when the tabs are pulled. A screwand socket combination 25 and 26 is attached to each tab, as illustratedin FIG. 1B, to facilitate the gripping and pulling of the tabs.

An appropriate length is then measured and a heat gun applied to thetubing. Upon application of this heat, the tubing is stretched, yieldinga tapered end. The tip is then cut at a point where the inside diameterof the cannula approximates the outside diameter of the dilator whichwill be used with the particular cannula. This tapering method servestwo purposes. First, the outside diameter is tapered to facilitateinsertion of the cannula into the body. Second, a tight fit with theprobe at this end minimizes blood loss.

In one preferred embodiment of the present invention, the thickness ofthe structure from the inner surface to the outer surface is 0.010 inchwith a tolerance of plus or minus 0.002 inch. The required diameter ofthe cannula will vary with the diameter of various dilators which areused in combination with the sheath. It is estimated that useful sizeswill range from an inner diameter of 0.05 inch to an inner diameter of0.2 inches; however, there may be applications requiring larger orsmaller dimensions. The inner diameter tolerance is plus 0.002 inch andminus 0.000 inch.

In the preferred embodiment, the cannula is sterilized using ethyleneoxide and packaged with a sterilized percutaneous needle, a wire guide,and a dilator in a hermetically sealed plastic bag.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly a preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

The invention claimed is:
 1. A cannula comprisinga tubular structurehaving one end which has a pair of open ended slits, said tubularstructure being compatible for insertion within the body and having anopposite end adapted to be inserted in the body with said one endextending out of the body, said tubular structure being formed offlexible material having the physical property of molecular orientationwhereby a tear in said material runs readily only in a longitudinaldirection along the length of said tubular structure, said tubularstructure being flexible from its inner diameter to its outer diameterand continuously smooth on its inner surface and outer surface, saidslits each having a closed end located between said one end and saidopposite end; a first tab defined by said slits on one side of one endof said tubular structure; and a second tab defined by said slits on theother side of said one end of said tubular structure whereby when saidtabs are pulled apart, said structure tears longitudinally along itslength beginning at said closed ends and extending to the opposite endof said tubular structure.
 2. The cannula of claim 1 in which theflexible material is a plastic.
 3. The cannula of claim 1 in which theflexible material is polytetrafluoroethylene.
 4. The cannula of claim 1in which said opposite end is tapered so as to define a tapered endportion, said tubular structure having an inner surface and an outersurface and having a substantially uniform thickness from the innersurface to the outer surface except at the tapered portion.
 5. Thecannula of claim 1 in which said tabs are integral with said tubularstructure and are separated by said open ended slits.
 6. A cannula kitcomprising:a cannula including a tube of flexible material having thephysical property of molecular orientation whereby a tear in saidmaterial runs readily only in a longitudinal direction along the lengthof the tube, said tube being soft and flexible from its inner diameterto its outer diameter; a first tab on one side of one end of said tube,a second tab on the other side of said one end of said tube whereby,when said tabs are pulled apart, said tube tears longitudinallyseparating said tube from any object within said tube; a percutaneousneedle; a wire guide; a dilator; and a bag containing said cannula,guide and dilator.
 7. The cannula kit of claim 6 where said bag ishermetically sealed and made of plastic.
 8. A cannula comprising:atubular structure having one end which has a pair of open ended slits,said tubular structure being compatible for insertion within the bodyand having an opposite end adapted to be inserted in the body with saidone end extending out of the body, said tubular structure beingcontinuously smooth on its inner surface and outer surface, means forallowing the opposite end to remain continuously smooth on its innersurface and outer surface while the opposite end is within the body,said means for allowing including said tubular structure being formed offlexible material having the physical property of molecular orientationwhereby a tear in said material runs readily only in a longitudinaldirection along the length of said tubular structure, a first tabdefined by said slits on one side of said one end of said tubularstructure; and a second tab defined by said slits on the other side ofsaid one end of said tubular structure whereby, when said tabs arepulled apart, said structure tears longitudinally along its lengthbeginning at said slit closed ends and extending to the opposite end ofsaid tubular structure.
 9. A removable cannula for introducing a memberinto an internal organ of the body, said cannula comprising:(a) atubular structure compatible for insertion within the body, said tubularstructure having one end and having an opposite end adopted to beinserted into the body with said one end extending out of the body, saidtubular structure being flexible from its inner diameter to its outerdiameter, said tubular structure having an internal passageway forpassage of a member into an internal organ of the body; and (b) removalmeans for removing said cannula from about the member after theintroduction of the member into the body through the internal passagewayof said tubular system, said removal means including means for providingfor the inserted portion of said tubular structure to remaincontinuously smooth on its inner surface and its outer surface duringinsertion, said removal means including:(i) said flexible materialhaving the physical property of molecular orientation whereby a tear insaid material runs readily only in a longitudinal direction along thelength of said tubular structure, (ii) said one end of said tubularstructure having a pair of open ended slits, said slits having closedends located between said one end and said opposite end,(iii) a firsttab defined by said slits on one side of said one end of said tubularstructure and (iv) a second tab defined by said slits on the other sideof said one end of said tubular structure whereby, when said tabs arepulled apart, said structure tears longitudinally along its lengthbeginning at said closed ends of said slits and extending to theopposite end of said tubular structure. .Iadd.
 10. A cannula kitcomprising:a tube of flexible plastic material compatible for insertionwithin the body and having the physical property of molecularorientation whereby a tear in said material runs readily only in alongitudinal direction along the length of the tube, said tube beingsoft and flexible from its inner diameter to its outer diameter; a firsttab on one side of one end of said tube, and a second tab on the otherside of said one end of said tube whereby, when said tabs are pulledapart, said tube tears longitudinally separating said tube from anyobject within said tube; and a dilator. .Iaddend. .Iadd.11. A cannulacomprising: a tube of flexible material compatible for insertion withinthe body and having the physical property of molecular orientationallowing a tear in said material to run readily only in a longitudinaldirection along the length of the tube, said tube being soft andflexible from its inner diameter to its outer diameter and tapered atone end adapted for insertion within the body; a first tab on one sideof the end of said tube opposite said one end and a second tab on theother side of said opposite end of said tube whereby, when said tabs arepulled apart said tube tears longitudinally separating said tube fromany object within said tube. .Iaddend. .Iadd.12. The cannula of claim 11wherein said tube is continuously smooth on its outer surface. .Iaddend..Iadd.13. The cannula of claim 12 wherein said tube is continuouslysmooth on its inner surface. .Iaddend. .Iadd.14. A cannula comprising: atubular structure having one end which has a pair of open ended slits,said tubular structure being compatible for insertion within the bodyand having an opposite end adapted to be inserted in the body with saidone end extending out of the body, said tubular structure being formedof flexible material having the physical property of molecularorientation allowing a tear in said material to run readily only in alongitudinal direction along the length of said tubular structure, saidtubular structure being flexible from its inner diameter to its outerdiameter, said slits each having a closed end located between said oneend and said opposite end; a first tab defined by said slits on one sideof one end of said tubular structure; and a second tab defined by saidslits on the other side of said one end of said tubular structurewhereby when said tabs are pulled apart, said structure tearslongitudinally along its length beginning at said closed ends andextending to the opposite end of said tubular structure without the needfor any mechanical means for facilitating longitudinal separation ofsaid tube. .Iaddend. .Iadd.15. The cannula of claim 14 in which saidtubular structure is continuously smooth on its outer surface. .Iaddend..Iadd.16. A cannula comprising: a tube of flexible plastic materialcompatible for insertion within the body and having the physicalproperty of molecular orientation whereby a tear in said material runsreadily only in a longitudinal direction along the length of the tube,said tube including a non-mechanical means for longitudinally tearingapart said tube, said tube being soft and flexible from its innerdiameter to its outer diameter; a first tab on one side of one end ofsaid tube, and a second tab on the other side of said one end of saidtube whereby, when said tabs are pulled apart, said tube tearslongitudinally solely due to said non-mechanical means, separating saidtube from any object within said tube. .Iaddend.